An inherent characteristic of a refrigerant compressor, such as used in an automotive air conditioning system, is the generation of dynamic pressure fluctuations, or pulsations, due to the dynamics of the compression process and interaction of the gaseous refrigerant flow between the cylinders in the compressor. These pressure pulsations have the undesirable effect of exciting certain components in the automotive air condition system, as well as components in the vehicle structure, which result in objectionable noise and/or vibration. Also, the vibrating and rattling components are prone to more rapid wear and premature failure.
The prior art attempts to solve this problem by installing a pressure pulsation muffler in the discharge conduit extending from the compressor to the air conditioning condenser. However, the in-line mounted mufflers are expensive and require considerable additional space.
The prior art also teaches that pressure pulsations may be attenuated by enlarging the volume of the compressor discharge plenum, or cavity, which, due to the expansion characteristics of refrigerant gas, will act to absorb some of the pressure pulsations. However, this prior art attempt to alleviate the pressure pulsation problem is also undesirable because an enlarged discharge cavity for the refrigerant compressor requires additional space and significantly increases the cost of the compressor.
Further, as perhaps best illustrated in the U.S. Pat. No. 4,715,790 to Iijima et al, issued Dec. 29, 1987, the prior art has attempted to alleviate the pressure pulsation problem by adding a gas flow restriction within the discharge cavity. The restriction comprises a reduced size orifice through which the refrigerant gas is required to flow. At low compressor operating speeds, where the pressure in the discharge cavity is relatively low, this method works satisfactorily. However, the disadvantage of this method of pulsation attenuation becomes highly evident at high compressor operating speeds. During high speed operation, the added pressure drop in the discharge cavity due to the orifice significantly increases the discharge pressure within the charge cavity. In fact, the pressures in the discharge cavity become so high at high operating speeds that the critical limit of the surrounding materials is often approached, thereby significantly reducing the durability of the compressor.